Anhalonium retusum (Ariocarpus retusus) Photo by: Valentino Vallicelli( Living Rock or Seven Stars ) Only the leaf-like rosette of tubercles is visible on this plant. This is the largest species of the genus. It is also one of the easiest and fastest to grow. It might still take 6-10 years, to go from seeds to flowering size.

Origin and Habitat: Ariocarpus retusus is widely distributed from north of Saltillo, Coahuila southwards to San Luis Potosi. Also found occur in Tamaulipas and Zacatecas.Altitude range: High Chihuahuan desert at altitudes of between 1300 and 2000 metres above sea level. This species grows at lower altitudes (around 200 - 800 metres) of the Sierra Madre Oriental it is replaced by Ariocarpus retusus ssp. trigonus.Habitat: The species tends to favour limestone and rocky slopes in semi-desert vegetation. The original range of this species extended from Coahuila and Nuevo León in the north to San Luis Potosí in the south. However, much of this range has been modified by agricultural development. A. retusus is a perennial and obligate gypsophile, occurring regularly in Muhlenbergia grassland and Bouteloua grassland in Central Mexico. Ariocarpus species are the only succulents present in the Muhlenbergia grassland. Although A. retusus has a relatively extensive area of distribution and a large population, it has a very low density. It is a slow growing species. This species is threatened by illegal collecting and agricultural development, however, they do not represent major threats. It is found in commercial cultivation.

Description:Ariocarpus retususus commonly known as the "Star Rock" is one of the largest species that distinguishes for the fat triangular tubercles forming a starry rosette. It is a widespread and extremely variable plant. Tubercle size and shape vary widely, a terminal areole is sometimes present at the tip. The vast amount of phenotypic variation in the species has led to the erection of several variants and has received numerous unnecessary names of no botanical value.Habit: Solitary, slow growing geophyte cactus with tubercles slightly projecting above ground level. The flat tuberous body is below the soil.Stem: Grey, or blue-green, flattened, globose, rounded on top, 3-12 cm high, 10-25 cm in diameter.Tubercles: Leaf-like, divergent, erect, basally compressed, usually becoming attenuate at the apices, convex or nearly flattened adaxially and often with shallow adaxial undulations or wrinkling, not fissured, 1,5-4 cm long, 1-3,5 cm wide, nearly as wide as long.Areoles: At the tips of the tubercles, rounded, 1-5 mm in diameter often only on younger specimens.Flowers: Diurnal 4-5cm in diameter, 2-4,2 cm long, white to pink (or magenta), occasionally with reddish midribs.Roots: Tap root.Flowering time: Autumn.Fruits: White, green, or rarely pinkish, 10-25 mm long, 3-10 mm in diameter.Remarks: All of the Ariocarpus seedlings are spiny and quite different from adult specimens, though the spines are feather-like.

Subspecies, varieties, forms and cultivars of plants belonging to the Ariocarpus retusus group

Ariocarpus confususHalda & Horáček: intermediates between Ariocarpus retusus and Ariocarpus trigonus flower color, white through to magenta, a color not found in any other populations. Distribution: Aramberri region.

Ariocarpus retusus subs. pectinatusWeisbarth: It has, dull pectinated spines already present in young specimens up to 1,2 to 2,0 mm long. The spines persist with the age. Areoles at the tips and extending on the upper side of the tubercles, elongated 2 to 20 mm long, wooly.

Ariocarpus retusus cv. Mituibo: (a.k.a. cv. Three Finger or Tresfinger)The tip of each tubercles is split into three points as three fingers, a bit like a trident with a large central section and two smaller ones on each side.

Ariocarpus retusus cv. Tama Botan: (a.k.a. Ariocarpus retusus var. major) It is a cultivated selection with very wide leaflike, divergent tubercles. The tubercles are 3,5 to 5 cm wide, and are as wide as long or wider in adult specimens.

- ( Living Rock or Seven Stars ) Only the leaf-like rosette of tubercles is visible on this plant. This is the largest species of the genus. It is also one of the easiest and fastest to grow. It might still take 6-10 years, to go from seeds to flowering size. (Ariocarpus retusus)Photo by: Andrea B.

Cultivation and Propagation: This species is slow growing but certainly not as slow as some other types of cacti, it is of easy culture in a well drained, non-organic, free-draining soil compost, with ample water during the growing season. Use of a weak low-nitrogen fertilizer during the growing season can encourage growth. The main threat to their development is root rot. Ariocarpus should be kept dry whenever there is a threat of cold. The appearance of Ariocarpus can benefit greatly by watering the plants from the bottom. This practice will help to keep the “wool” on the top of the plant from becoming matted or discoloured. Need light shade to full sun. Frost Tolerance: Hardy to -10° C.Propagation: It is probably the easiest species of the genus to raise from seed, but will generally take about 6-10 years to reach flowering size, occasionally grafted.